Millions in Kolkata, Mumbai at immediate risk from rising seas, UN report says

Millions of people in Kolkata and Mumbai are at “immediate risk” of losing their homes to permanent inundation as sea levels rise, according to a United Nations report released on Monday.

The report by the UN Secretary-General, titled “Challenges related to sea level rise and ways and approaches to address it”, said rising seas are already damaging infrastructure, water systems, transport networks, energy grids, buildings and groundwater resources, with consequences for human rights, development and financial stability.

In low-lying South Asian deltas, including Kolkata and Mumbai, the main threat is human displacement. More than 14 million people across cities including Kolkata, Mumbai and Dhaka are at immediate risk of losing their homes to permanent inundation, the report said.

The risks differ by region. In high-income coastal cities such as Miami, New York and Guangzhou, coastal infrastructure faces an estimated $2 trillion to $3.5 trillion in assets at risk.

The report said sea level rise is also threatening public health through damage to health and sanitation infrastructure, increased water-borne diseases, disrupted sanitation and greater risks of injury and death. Rising seas can push saltwater into freshwater wells and soils, affecting drinking water, agriculture, irrigation and groundwater-dependent ecosystems.

Nearly 770 million people, around 10% of the global population, live in coastal areas less than five metres above the high tide line and face acute risks.

Global sea levels rose at an average rate of 4.7 mm annually between 2014 and 2023. In 2024, the rate reached 5.9 mm, a record driven primarily by exceptional ocean warming. The annual rate between 2012 and 2025 was 4.75 mm, while 2025 levels remained comparable with the 2024 record high.

The UN attributed accelerating sea level rise primarily to melting glaciers and the thermal expansion of warming oceans caused by human-induced global warming.

The report warned that the combination of rising seas and land subsidence is intensifying flooding, erosion, ecosystem degradation and displacement. It called for early and long-term adaptation planning, stronger scientific and institutional capacity, and predictable financing, particularly for communities and countries most at risk.